release of mercury during leaching of fly ash
TRANSCRIPT
i
RELEASE OF MERCURY DURING LEACHING OF FLY ASH
An Honors Thesis
Presented in Partial Fulfillment of the Requirements for
Graduation with Distinction in the
College of Engineering at The Ohio State University
By
Ellen Regennitter
*****
The Ohio State University 2007
Honors Thesis Examination Committee: Approved by Dr. Harold Walker, Advisor
Dr. Linda Weavers Harold Walker Adviser Undergraduate Program in
Engineering
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ABSTRACT
Fly ash created in the generation of energy contains mercury. Currently, the most
accepted use for fly ash is as an inexpensive alternative to Portland cement in concrete
mixtures. Because of new mercury-air standards, determining the affect of mercury
within concrete structures is important. Analyzing the make-up of the fly ash, then, is
used in this research concept to gain an understanding of the impact of the chemical
make-up of fly ash on a concrete structure. Pinpointing the fly ash - concrete interaction
and synthesizing the characteristics demonstrated in a concrete containing fly ash
ultimately leads to a perception of the release of mercury from these materials in their
final state. Leachate tests were preformed to simulate the release of mercury from fly ash
samples in Municipal Solid Waste Landfills and Construction Landfills. The results of
these analyses led to the determination of the limited short and long-term release of
mercury from the samples and these conclusions lead to a basic understanding of the
impact fly ash sample release of mercury can have on concrete structures.
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Dedicated to my family
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ACKNOWLEDGMENTS
I wish to thank my adviser, Dr. Hal Walker, for guidance, support, encouragement
and patience for allowing me to gain time management experience and emphasizing the
importance of learning in a hands-on environment.
I thank Dan Golightly for introducing me to work in the laboratory and initially
developing my comfort level in this working area.
I am grateful to Ryan Mackos for spending long hours helping me to finish all
research analysis. Without his help, none of these conclusions could have been reached.
v
VITA
September 17, 1984……………………………Born – West Des Moines, Iowa
2003……………………………………………Engineering Design Intern, The Ohio Department of Transportation, District 12
2004 – 2006……………………………………Engineering Line Design Intern, American Electric Power 2002-present……………………………………Undergraduate Student and Researcher,
The Ohio State University
PUBLICATIONS
Not Applicable
FIELDS OF STUDY
Major Field: Structural Engineering
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TABLE OF CONTENTS
Page
Abstract……………………………………………………………………….ii
Dedication…………………………………………………………………….iii
Acknowledgments…………………………………………………………….iv
Vita……………………………………………………………………………v
List of Tables………………………………………………………………….viii
List of Figures…………………………………………………………………ix
Chapters:
1. Introduction………………………………………………………..1
2. Test Methods………………………………………………………5
2.1 Concrete and Fly Ash………………………………………….5
2.2 Fly Ash Elemental Composition, Samples and Mercury Content in
Concrete Ingredients…………………………………………...10
2.3 Experimental Setup and Leaching Testing…………………….14
2.4 Inductively Coupled Plasma Atomic Emissions Spectrometry..16
2.5 Varian SpectrAA Testing………………………………………17
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3. Test Results and Discussion……………………………………….19
3.1 Fly Ash Characterization: Sampling, Sample pH testing, Total Dissolved
Solids Test…………………………………………………….19
3.2 Sample Analysis……………………………………………….29
4. Conclusions and Recommendations……………………………….38
4.1 Conclusions…………………………………………………….38
4.2 Recommendations……………………………………………...39
5. References………………………………………………………….41
6. Appendix……………………………………………………………43
viii
LIST OF TABLES
Table Page 2.1 Elemental Composition of Fly Ash Samples……………………………….11
3.1 TCLP and SPLP Data for Fly Ash Leachate Samples……………………...37
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LIST OF FIGURES
Figure Page 2.1 Fly ash beads at the microscopic level……………………………………….7
2.2 Usage of Coal Combustion Products………………………………………....8
2.3 Production and Usage of Coal Combustion Products…………………………9
2.4 Potential Uses of Coal Ash By-Products……………………………………..10
2.5 Summary of processes for classification of fly ash…………………………..13
2.6 Rotator Device for TCLP and SPLP testing………………………………….16
3.1 Initial Leachate Data for TCLP Method………………………………………20
3.2 Initial pH Data for SPLP Method……………………………………………..21
3.3 18 Hour Total Dissolved Solids Data for TCLP………………………………22
3.4 18 Hour Total Dissolved Solids Data for SPLP………………………………23
3.5 7 Day Total Dissolved Solids Data for TCLP………………………………...24
3.6 7 Day Total Dissolved Solids Data for SPLP…………………………………25
3.7 18 Hour pH Data for TCLP……………………………………………………26
3.8 18 Hour pH Data for SPLP…………………………………………………….27
3.9 7 Day pH Data for TCLP………………………………………………………28
3.10 7 Day pH Data for SPLP………………………………………………………29
3.11 TCLP Analyte Concentration for AEP Mountaineer Fly Ash Sample………...31
x
3.12 SPLP Analyte Concentration for MER 0357 Fly Ash Sample………………...32
3.13 Mercury Concentration for TCLP Extraction #1……………………………….33
3.14 Mercury Concentration for TCLP Extraction #2……………………………….34
3.15 Mercury Concentration for SPLP Extraction #1………………………………..35
3.16 Mercury Concentration for SPLP Extraction #2………………………………..36
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CHAPTER 1
INTRODUCTION
Coal fly ash is produced as a byproduct of energy generation. As coal- fired
boilers generate electricity, fly ash and flue gas desulfurization byproducts are created.
In the process of energy generation, mercury is volatized and converted to elemental
mercury at the very high temperatures located within coal- fired utility boilers (EPA,
2000). A portion of this mercury is re-oxidized as the flue gas is cooled. As conversion
from gaseous elemental mercury to HgCl2 and HgO occurs, the mercury is effectively
captured in fly ash material (EPA, 2000). HgCl2 is effectively captured during this
process with SO2 control, but because some mercury forms that are created are more
difficult to remove, it is important to understand the effect of their volatility and limited
solubility. Once formed, fly ash can be utilized as an inexpensive alternative to Portland
cement in concrete, as it has been found to enhance certain desirable properties in freshly
prepared and hardened concrete.
Electrical power generator production of fly ash is approximately 15% of the fly
ash that is incorporated into structural concretes and grout (American Coal Ash
Association, 2002). Once included in the concrete mix, fly ash reduces the water
2
requirements of the concrete mixture. A concrete made with fly ash also has increased
workability, reduced heat of hydration and a reduced air content. After the concrete has
cured, it has an increased compressive strength as a product of the reduced water content.
Typically, the fly ash concrete will have lower absorption and permeability and generally
improved defense against sulfate attack. Concrete is a porous material and mercury
bound to fly ash ultimately may be released following concrete placement. In addition to
the prolonged threat of mercury release is an initial potential for release through the
mixing, pouring, curing and temperature increase of concrete. In any of these processes,
the temperature of fly ash could increase the volatization and release of mercury from the
concrete material.
Recently, the presence of mercury in fly ash material has been a topic of great
importance based on the announcement of the Clean Air Mercury Rule. The rule, which
is expected to come into effect in 2007, will significantly impact the reuse initiatives of
coal combustion byproducts. Because fly ash contains mercury, especially when
activated carbon injection is used as a means to achieve greater mercury reductions in
generation, it is important to understand the impact of mercury levels in fly ash concrete
applications. As mercury emissions controls are brought on-line, an increase in the
amount of mercury contained in fly ash is expected, and because concrete is a porous
material, the mercury bound to fly ash may ultimately be released to the atmosphere.
Because mercury is a well known neurotoxin, it is important to determine the fate
of mercury in concrete. Therefore, the objectives of this research analysis are to identify
the analyte makeup of typical fly ash samples and to determine the extent to which
leaching releases mercury from fly ash to the atmosphere. In previous work, the gaseous
3
release of mercury during curing of concretes was determined. In this study,
investigation continues to examine the leaching of mercury to water during disposal and
reuse of fly ash. The project centered around identifying the sample characteristics of fly
ash specimens and analysis of their effects on mercury release. Leaching data was
modeled using geochemical speciation methods to develop a better understanding of the
roles of different solid phases in controlling the solution of chemistry of the leachate.
The observations can then be correlated to the effects of fly ash utilized in concrete
applications. Using two specific leach testing methods, fly ash samples were tested for
reactions in landfills and reactions under acid rain conditions.
First, five different samples of fly ash were selected. Each sample of fly ash was
created in a generation facility from a different location which could have had an affect
on the level of mercury in the sample. The different fly ashes were then used in typical
leachate testing procedures to synthesize the natural affects of rain water and landfill acid
on the sample. The fly ash - leachate solutions were then analyzed using a Varian
SpectrAA to determine the mercury in each sample. The solutions were also subjected to
an Inductively Coupled Plasma Atomic Emissions Spectrometry test to determine the
additional analyte make-up of the samples. In the end, the data collected from these tests
were manipulated to determine if the effects of the mercury and additional analyte
material in the fly ash could pose a threat to health if released through naturally occurring
leaching.
This report is organized as a thorough investigation of fly ash, the elemental
composition of the samples, the mercury content in the concrete ingredients and the result
of that elemental makeup. The leaching test procedures are then discussed as an example
4
of two ways that fly ash elemental makeup can leach into the water supply. The
discussion will also serve as an attempt to prove the adequacy of this analysis for
assessment of environmental impact. Finally the test methods and test results for the
experiments are discussed and conclusions are drawn from the data collected.
5
CHAPTER 2
TEST METHODS
2.1 Concrete and Fly Ash
As one of several coal combustion by-products, fly ash is the finely divided
mineral residue resulting from the combustion of coal in electric generation plants.
Because fly ash is an inorganic incombustible matter present in the coal, it becomes fused
during combustion into an amorphous structure. Once burned, fly ash becomes
suspended in exhaust gas as a solidified material and typically is collected by electrostatic
precipitators. Generally, fly ash particles are cylindrical and range in size from .4
micrometers to 100 micrometers. Fly ash particles are comprised mostly of aluminum
oxide, silicon dioxide, and iron oxide. Because they are pozzolanic, they react to form
cementious material. In 1996, America’s coal- fired power plants produced 53 million
tons of fly ash. Although the chemical and physical properties of coal ash make it ideal
for a variety of engineering applications, it must compete against other inexpensive bulk
materials like sand and gravel. As a result, there are only certain areas where it is
economically advantageous to transport and handle the fly ash. About three-quarters of
the fly ash produced in the United States is not recycled for commercial use. Instead, the
fly ash is placed in a specifically designed landfill. To prevent environmental impacts,
landfill sites are carefully chosen to avoid flood plains and wells are typically installed
around the site so that the quality of the surrounding water can be routinely inventoried.
6
Fly ash that is recycled is utilized in several different ways. Power plant fly ash is
used in autoclaved aerated concrete blocks, liquid fixation, blasting grit, highway ice
control, masonry blocks, concrete admixture, as material in lightweight alloys, roadway
and runway construction, flowable fill material, roofing granules, grouting and structural
fill. Fly ash is used as a high-performance substitute for Portland cement and sometimes
as an addition to the clinker which is ground to form Portland cement. The material can
replace up to 50% of Portland cement by mass in concrete and changes the chemical
make-up of the concrete mix in several different ways which can lead to higher final
strength and reduced risk of chemical corruption. Replacing Portland cement with fly ash
also decreases the greenhouse gas signature of concrete by reducing carbon dioxide
production. Coal fly ash has been used around the world as an ingredient of concrete for
60 years and many United States suppliers routinely use fly ash in concrete mixtures.
The ash is processed into pellets that make it more readily utilized as an aggregate in
concrete as well.
Most health-related fly ash concerns focus on the potential health risk of
inhalation, ingestion, direct contact or exposure to trace elements. Coal fly ash particles
are essentially insoluble aluminosilicate glasses, however trace substances on the ash
surface may still be soluble. Water, acid rain and other liquids can percolate through ash
and dissolve, or leach, trace elements from the ash. The analyte make-up could then
potentially reach a drinking water source such as groundwater, rivers or lakes.
Suspended particles would be removed from the water through filtration at water
treatment plant; however, the dissolved elements would not be removed through this
process.
7
Recycling fly ash in products and construction carries many benefits – and the
focus of this study has been to rule out potential hazards from this recycling process so
that barriers to re-use of fly ash are minimized. Using coal ash as cement can mean that
the process consumes less energy and limestone than production of conventional
cement – and avoiding electricity production lessens overall emissions. In addition,
carbon dioxide emissions from cement kiln firing are reduced in direct proportion to the
amount of ash substituted in a concrete mix.
Figure 2.1: Fly ash beads at the microscopic level
8
Figure 2.2: Usage of Coal Combustion Products
9
Figure 2.3: Production and Usage of Coal Combustion Products
10
Figure 2.4: Potential Uses of Coal Ash By-products 2.2 Fly Ash Elemental Composition, Samples and Mercury Content in Concrete Elements
Five different coal fly ash samples were utilized in this research study. The fly
ash was classified as Class F and it originated from eastern bituminous coal combusted
electrical utilities. Class F fly ash is characterized for the content, specific surface area
and loss of ignition values. As required by ASTM, Class F fly ash should have an LOI
less than 6%. The concentrations of SiO 2, Fe2O3 and Al203 must be greater than 70%. In
a previous study, the elemental composition of the fly ash was verified using Cold Vapor
11
Atomic Adsorption Spectrometry and Cold Vapor Atomic Fluorescence Spectrometry in
determining the mercury and inductively coupled plasma – atomic emission spectrometry
to verify the concentrations of silicon, iron, aluminum and sulfur.
Elemental Composition Concentration (%) Aluminum 15.1 Barium 0.3 Calcium 2.4 Iron 2.3 Magnesium 0.7 Potassium 1.5 Silicon 26.9 Sodium 0.7 Sulfur 0.1 Zinc 0.1 Arsenic 16.6 Cadmium 2.5 Cobalt 34.8 Chromium 129 Copper 127 Lead 27.2 Lithium 197 Manganese 129 Mercury 0.117 Molybdenum 15.1 Nickel 84.7 Phosphorus 930 Selenium 18.8 Strontium 75
Table 2.1: Elemental Composition of Fly Ash Samples As the demand for finer, more accurately sized fly ash grows, classification
methods for fly ash ingredients have become more sophisticated. Generally speaking,
most powders are the result of a comminution process that creates a combination of fly
ash samples which dictate characteristic hardness or abrasive nature of the material.
12
There are a range of machines available for the comminution process and each has its
own particular ability to break compounds through compression, impact or attrition.
Therefore the classification of dry powders using conventional sieving techniques
becomes progressively more important. For a given classified sample, the specific
gravity of materials and the separation or cut size moves the sample up or down the
classification scale. There are many reasons to classify the fly ash produced through
electrical generation and the criterion can range from simply the size of the largest
particle to the decorative finish or surface coating of the materials. Because the ASTM
codes have a very heavy emphasis on the chemistry of fly ash and the chemistry of fly
ash is highly dependent on the mineralogy and particle size, it is therefore important to
understand this classification process and the impact of the particle size.
There are two parameters that determine the reactivity of fly ash – mineralogy and
particle characteristics. Particles are mostly glassy, solid, and spherical in shape and
there may also be unburned carbon present depending on burn efficiency. Particles of fly
ash range in size from 1 to 10 microns and regardless of the type of classification, the ash
will contribute to the 7 and 28 day strengths of concrete.
To determine elemental concentrations of the samples before leaching tests were
preformed, a solution of fly ash was prepared in a microwave-heated digestion method of
a closed vessel containing 300mg of fly ash and an acid mixture of nitric, hydrochloric
and hydrofluoric acids. (EPA 2000) The Varian VISTA was calibrated using matrix
matched sample solutions and the concentrations of each test produced background-
corrected relative intensities for the 9 spectral lines that correlate with aluminum, iron
and silicon for a simultaneous available emissions of 1.2kW plasma.
13
The classification of fly ash is important in the selection of ash that is used in
concrete mixtures and each different classification can mean something different for the
mercury content of the samples. Fly ash is most beneficially used as a plasticizer, and the
charged cement particles tend to break bonds and flocculate. This action is different than
the normal effect of cement in concrete which disperses through cement particles and
tends to adsorb to surfaces and act as a repellent. Certain types of reactive fly ash
particles act as a very powerful repellent which because of their charges and dependent
on the presence of reactive crystalline phases in the ash.
Figure 2.5: Summary of processes for classification of fly ash
Previous experiments were designed to determine the background mercury
concentration in Portland cement. The analysis was conducted using a Varian Hot Block
and samples were digested and then transferred to high-density polyethylene bottles and
14
subjected to Cold Vapor Atomic Adsorption Spectrometry and Cold Vapor Atomic
Fluorescence Spectrometry testing. The intent of this project was to submit the fly ash to
a similar test to determine the extent of release of mercury, iron, silicon and sulfur, which
is found in the chemical makeup, to the environment during leaching.
2.3 Experimental Setup and Leaching Testing
Leaching tests serve to quantify the source terms for fate and transport modeling.
The purpose of the testing is to obtain aqueous phase concentrations of constituents
which are released from solids when placed in a land disposal unit. The underlying
assumption is that if the constituent does not leach from the waste, then land disposal of
that constituent is not a threat to groundwater. Toxicity characteristic leaching procedure
(TCLP) and synthetic precipitation leaching procedure (SPLP) have been widely used to
generate leachate concentrations for all types of solids for both organic and inorganic
constituents. The assumption is that potentially hazardous wastes comprise at most 5%
of the volume of the material deposited in municipal solid waste landfills. The municipal
waste is assumed to degrade and produce an acidic liquid to which the waste is exposed.
Thus, a 5%/95% relationship leads to the specific composition of the acetic acid solution
used in the TCLP test.
To separate forms of leaching, test procedures exist that are applicable to a study
focusing on the effects of fly ash in the environment. The toxicity characteristic leaching
procedure (TCLP) works to determine the mobility of organic and inorganic analytes in
solid wastes. The TCLP test method is utilized in this project when the liquid fractions of
the TCLP extract indicated a regulated compound was present. In this method, the fly
15
ash samples are subjected to 18 hour and 7 day interaction with the leaching solution.
For liquids containing .5% solids, the liquid was separated from the solid phase using a
filtration device and then stored for analysis. The leaching solution in this method is a
mixture of glacial CH3CH2OOH, reagent water, and NaOH. The solution is diluted to a
volume of 1 liter and made to have a pH of 4.93. This method also places requirements
on the minimal size of the field sample, depending on the physical state of the waste.
Immediately after TCLP extracts are extracted, the samples were prepared for analysis as
specified in the procedure. Samples are allowed to be refrigerated, and were refrigerated
in this project following preparation for analysis. After all samples were gathered for
analysis, the ICP-AES and SpectrAA analyses were utilized. The method was completed
in duplicate.
Synthetic Precipitation Leaching Procedure (SPLP) is designed to simulate a
monodisposal of waste and reveal the soluble phases of a sample being tested. The test
aids in predicting the geochemical effect of a “flush” on a material and the extraction
liquid used in this method is similar to the TLCP method; however, it mirrors the effects
of precipitation leaching rather than municipal landfill leachate. Static leaching tests, like
these, are short term tests and involved agitating samples using a rotator device and then
sampling the resulting solution. The SPLP test is a method designed to predict and
determine the potential for leaching metals into ground and surface waters and uses a
1:20 liquid to solid ratio. There is a rigorous leach of the material (for 18 hours and 7
days) and the extraction fluid is intended to simulate precipitation which occurs naturally
east of the Mississippi river as a fluid slightly acidic to reflect industrialization and air
pollution impacts on precipitation.
16
Figure 2.6: Rotator Device for TCLP and SPLP testing 2.4 Inductively Coupled Plasma Atomic Emissions Spectrometry (ICP-AES)
Flame spectroscopy, the distinctive optical colors that are produced when
compounds of certain metals are vaporized in flames, is a highly sensitive and specific
means of identifying minute quantities of certain elements in materials. Optical emission
spectrometry developed into a powerful method of chemical analysis and in these
developments, the concentration of a specific element in a sample can be related to the
intensity of lines in its optical spectrum. Modern inductively coupled plasma atomic
emissions spectrometry relies on the same principles as flame spectrometry and
determines minute amounts of a very wide range of elements even in the presence of
much greater quantities of other elements. In analyzing samples, the inductively coupled
plasma atomic emissions spectrometry machine relates the chemical solution samples to a
set of calibrating standard. Each standard contains an accurately known concentration of
analyte element and a range of concentration for each element in the set is chosen to
17
include the expected concentration of that element in the sample solutions. The
calibrating solutions and sample solutions are sprayed into the plasma which is created in
the machine using Argon, and the intensities of appropriate emission lines are recorded.
The concentrations of the element in each sample solution are determined from the
calibrating graphs.
The plasma used in this method for analysis is simply a gas whose properties are
influenced by the presence of a significant concentration of ions and electrons. These
exist in approximately equal numbers over the volume of the plasma, so overall electrical
neutrality is maintained. ICP instrumentation relies on the used of the tesla coil to ignite
the plasma and then inject the sample flow into the base of the plasma. The bench top
ICP-AES is the third generation of ICP instrumentation and coordinates usage of
computer control, innovative optical design and lower argon and power consumption
over the life of the machine. The sample introduction system transports the analytes of
interested to the excitation source that causes the sample to undergo desolvation and
excitation resulting in emission of characteristic radiation. Due to the high temperature
of the ICP, singly charged ions dominate and the spectrometer separates the radiation of
interest so that the detection system measures the intensity of the selected radiation as
compared to the standard.
2.5 Varian SpectrAA Testing
Samples were also analyzed by the Varian SpectrAA 880Z Zeeman Atomic
Absorption Spectrometer (AAS). Because all atoms can absorb light in certain
wavelengths, these wavelengths can identify an atomic spectra based on characteristic
18
spectroscopic lines. Wavelengths are sharply defined and when a range of wavelengths is
surveyed and compared, lines which originate in the ground state atom are most often of
interest in atomic absorption spectroscopy and are called resonance lines. With particular
spectroscopic characteristics, each element comprises a number of discrete lines. Using
atomic absorption spectroscopy in conjunction with the analysis of this experiment
therefore allows analyte elements in a leachate solution to be compared spectroscopic ally
to calibration solutions enabling the concentration of analyte to be defined for a given
sample. Using the Beer-Lambert Law to define a relationship between analyte
concentration and light absorption, it can be seen that increased sensitivity can be
achieved in electrothermal atomization – in the case of this experiment, allowing the
mercury concentration in a sample of fly ash to be more highly detected.
Graphite furnace atomic absorption has become a field of analytic chemistry
focused on determining very low levels of trace metals in a variety of sample types. In
this form of analysis, molecules and compounds are broken down to atoms and ions.
Because light absorption or emissions is in discrete energy packets, the different in
energy between the energy levels is inversely proportional to the wavelength of emitted
light. Using a hollow cathode lamp, a furnace creates and contains atoms in the light path.
Atom population is then exposed to HCL emission at the resonance wavelength and the
light transmission is measured and absorbance is calculated. The detection limit for
CVAAS is .1 parts per billion.
19
CHAPTER 3
TEST RESULTS AND DISCUSSION
3.1 Fly Ash Characterization: Sampling, Sample pH testing, Total Dissolved Solids Test
Testing procedures, including quality control, were conducted in accordance with
EPA Test Methods 1131 and 1132. First, fly ash samples were analyzed to ensure that the
particle size was less than 1.0cm. Two different leaching solutions were used to
complete the experiment. In this method, the fly ash samples were subjected to 18 hour
and 7 day interaction with the leaching solution. To do this, 100g of fly ash was
combined with 2 L of leaching solution to achieve an acceptable liquid-to-solution ratio.
The initial pH of the mixture was then determined to ensure the method requirements
were met. The leaching solution in the TCLP method is a mixture of glacial
CH3CH2OOH, reagent water, and NaOH. The solution is diluted to a volume of 1 liter
and made to have a pH of 4.93. In the SPLP method, the solution is sulfuric acid/nitric
acid (60/40 weight percent mixture) H2SO
4 /HNO
3 . To create the solution, 60 g of
concentrated sulfuric acid is cautiously mixed with 40 g of concentrated nitric acid.
20
Pre-Filtration Leachate pH Data for TCLP
4.926
4.927
4.928
4.929
4.93
4.931
4.932
4.933
AEP M
ountain
eer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH
Series1
Series2
Figure 3.1: Initial Leachate Data for TCLP Method
21
Pre-Filtration Leachate pH Data for SPLP
4.17
4.18
4.19
4.2
4.21
4.22
4.23
4.24
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH Series1
Series2
Figure 3.2: Initial pH Data for SPLP Method
The test utilized the rotation device to mix the samples for 18 hours and 7 days – tests
were conducted in duplicate and samples were taken as specified in the EPA procedures.
As stated in the method, samples for both tests may be refrigerated unless refrigeration
results in irreversible physical change to the waste. The samples were collected in
“store” type containers and refrigerated. Once ready for evaluation, extreme acre was
taken to minimize the loss of volatiles. Samples were collected and stored in a manner
intended to prevent the loss of volatile analytes and therefore the waste samples were
collected in Teflon- line capped vials. The extracts for metallic analyte determinations
were acidified with nitric acid to a pH less than 2. Immediately after sampling and prior
22
to this storing technique, the liquid was separated from the solid phase using a filtration
device. The solution was then tested for pH and total dissolved solid content.
18 Hour Total Dissolved Solids Data for TCLP
0
100
200
300
400
500
600
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
TD
S (
pp
b)
Extraction #1
Extraction #2
Figure 3.3: 18 Hour Total Dissolved Solids Data for TCLP
23
18 Hour Total Dissolved Solids Data for SPLP
0
200
400
600
800
1000
1200
1400
1600
1800
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
TD
S (
pp
b)
Extraction #1
Extraction #2
Figure 3.4: 18 Hour Total Dissolved Solids Data for SPLP
24
7 Day Total Dissolved Solids Data for TCLP
0
100
200
300
400
500
600
700
AEP Mou
ntaine
er
MER 03
57
MER 032
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
TDS
(pp
b)
Extraction #1
Extraction #2
Figure 3.5: 7 Day Total Dissolved Solids Data for TCLP
25
7 Day Total Dissolved Solids Data for SPLP
0
500
1000
1500
2000
2500
AEP Mou
ntaine
er
MER 03
57
MER 032
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
TDS
(pp
b)
Extraction #1
Extraction #2
Figure 3.6: 7 Day Total Dissolved Solids Data for SPLP
26
18 Hour pH Data for TCLP
0
2
4
6
8
10
12
14
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH
Extraction #1
Extraction #2
Figure 3.7: 18 Hour pH Data for TCLP
27
18 Hour pH Data for SPLP
0
2
4
6
8
10
12
14
AEP M
ounta
ineer
MER 0357
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH
Extraction #1
Extraction #2
Figure 3.8: 18 Hour pH Data for SPLP
28
7 Day pH Data for TCLP
0
2
4
6
8
10
12
14
AEP Mou
ntaine
er
MER 03
57
MER 032
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH
Extraction #1
Extraction #2
Figure 3.9: 7 Day pH Data for TCLP
29
7 Day pH Data for SPLP
0
2
4
6
8
10
12
14
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
pH
Extraction #1
Extraction #2
Figure 3.10: 7 Day pH Data for SPLP 3.2 Sample Analysis
To analyze the concentration of mercury and other analyte elements, the Atomic
Fluorescence spectroscopy method was used in addition to the Inductively Coupled
Plasma-Atomic Emissions Spectrometry technique as discussed earlier in this report.
Both of these experimental analysis procedures can be completed utilizing Minteq A2
computer modeling programs to compare experimental results and determine the
importance of different solid phases in controlling solution composition.
The ICP-AES utilizes a diffraction grating fixed in space at the far end of the
spectrometer. Rotation of the diffraction grating sequentially moves each wavelength into
the detector. The computer control ensures that the detector is synchronized with the
30
grating so that the intensity at the detector at any given time is correlated with the
wavelength being diffracted by the grating. Using standard spectroscopic techniques,
sequential ICP-AES can provided extremely flexible and rapid analysis of a number of
chemical elements. The spectrometer was flushed with N2 gas to improve the detection
limits of elements and to ensure quality with emission wavelengths that are severely
compromised by interference with air. This N2 flush, which is constantly maintained in
the instrument regardless of whether such elements are being analyzed, also protects the
optics from the corrosive aspects of the atmosphere, which are particularly acute at sea.
First, the machine was allowed to warm up for 30 minutes. Next, a zero-order check was
conducted. Zero-order is the term used to define when the grating within the
spectrometer behaves as a mirror, reflecting incoming light rather than refracting it into
several wavelengths. A zero-order check physically moves the diffraction grating to its
zero position, where all light is reflected. An autosearch is preformed next to allow the
spectrometer to identify an acceptable reference peak. The machine is calibrated using
standards and finally the test was completed. The TCLP leachate concentration of the
AEP fly ash sample and the SPLP leachate concentration of the MER0357 fly ash sample
provide examples of typical ICP-AES results for this experiment.
31
TCLP Analyte Concentration for AEP Mountaineer Fly Ash Sample
0
200
400
600
800
1000
1200
1400
Na Al K Ca Mn Fe Cu Pb
Sample
Co
nce
ntr
atio
n H
g (
ug
/L)
Figure 3.11: TCLP Analyte Concentration for AEP Mountaineer Fly Ash Sample
32
SPLP Analyte Concentration for MER 0357 Sample
-10000
0
10000
20000
30000
40000
50000
60000
70000
Na Al K Ca Mn Fe Cu Pb Hg
Sample
Con
cent
ratio
n ug
/L
Figure 3.12: SPLP Analyte Concentration for MER 0357 Fly Ash Sample
33
A lamp of desired wavelength and a PMT detector provide absorbance values
based on the amount of the element present. When compared to a generated standard
curve, the element of interest can be quantified. Detection limits for the instrument vary
according the element under consideration, but for the analysis of mercury content in fly
ash leachate samples the detection limits test returned a 99% confidence rating that the
Hg concentrations reported were are less than 0.2ppb as recorded in the tables below.
The data collected through this method gave a standard deviation of .012246.
Mercury Concentration for TCLP Extraction #1Fly Ash Samples
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
Co
nce
ntr
atio
n H
g (
ug
/L)
18-Hour
7-Day
Figure 3.13: Mercury Concentration for TCLP Extraction #1
34
Mercury Concentration for TCLP Extraction #2 Fly Ash Samples
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
Co
nce
ntr
atio
n H
g (
ug
/L)
18-Hour
7-Day
Figure 3.14: Mercury Concentration for TCLP Extraction # 2
35
Mercury Concentration for SPLP Extraction #1 Fly Ash Samples
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
Co
nce
ntr
atio
n H
g (
ug
/L)
18-Hour
7-Day
Figure 3.15: Mercury Concentration for SPLP Extraction #1
36
Mercury Concentration for SPLP Extraction #2 Fly Ash Samples
-0.8
-0.7
-0.6
-0.5
-0.4
-0.3
-0.2
-0.1
0
AEP M
ounta
ineer
MER 03
57
MER 03
2
NRT ID 10
17
Coal C
reek
Standa
rd
Sample
Co
nce
ntr
atio
n H
g (
ug
/L)
18-Hour
7-Day
Figure 3.16: Mercury Concentration for SPLP Extraction #2
37
TCLP # 1
Mass (grams)
Initial pH
18 Hour TDS 18 Hour pH 7 Day TDS
7 Day pH
AEP Mountaineer 100 4.932 325 5.315 338 5.47 MER 0357 100 4.931 467 11.64 564 11.934 MER 032 100.1 4.928 433 11.57 593 11.98 NRT ID 1017 100.1 4.93 497 11.9 547 12.156 Coal Creek 100.1 4.93 416 11.49 502 11.2 Standard N.A. 4.93 196 5.1 299 4.9 TCLP # 2 AEP Mountaineer 100 4.93 329 5.28 326 5.13 MER 0357 100.1 4.932 445 11.489 554 11.5 MER 032 99.9 4.929 429 11.57 585 12.3 NRT ID 1017 100 4.93 497 11.79 492 12.17 Coal Creek 100 4.931 498 11.56 476 11.806 Standard N.A. 4.93 2.8 5.06 2.7 5.3 SPLP # 1
Mass (grams)
Initial pH
18 Hour TDS 18 Hour pH 7 Day TDS
7 Day pH
AEP Mountaineer 99.8 4.22 231 9.97 240 9.56 MER 0357 99.9 4.23 1559 11.75 1858 11.91 MER 032 100.1 4.23 1335 11.75 1563 11.68 NRT ID 1017 100 4.2 1077 11.66 1495 11.66 Coal Creek 100.1 4.22 1463 11.74 1558 11.67 Standard N.A. 4.19 19.05 9.24 15 8 SPLP # 2 AEP Mountaineer 100 4.22 229 9.71 278 9.76 MER 0357 100.1 4.22 1134 11.66 1985 12.24 MER 032 100.1 4.2 1307 11.82 1529 11.92 NRT ID 1017 100 4.19 1227 11.74 1567 11.99 Coal Creek 100.1 4.22 1469 11.81 1640 11.91 Standard N.A. 4.21 14 9.01 12 8.29
Table 3.1: TCLP and SPLP Data for Fly Ash Leachate Samples
38
CHAPTER 4
CONCLUSIONS AND RECOMMENDATIONS
4.1 Conclusions
Data from these laboratory experiments on fly ash samples suggests that release
of mercury from fly ash subjected to leachate solutions such as those found in municipal
landfills and natural precipitation is low and almost undetectable through modern testing
technology. Mercury release from samples subjected to both SPLP and TCLP testing
methods returned negative results through atomic absorption analysis and this
phenomenon exists only when mercury levels in samples are so low that the analysis is
barely sensitive enough to detect the element. The additional analyte elements identified
in the ICP-AES analysis of data ensures that fly ash material used in concrete, once
subjected to leaching, are not harmful. This study has shown that even where some
leaching of fly ash has occurred, its effects do not pose public health risks. The study has
proven that the fly ash ingredient utilized in several concrete applications does not add
potential mercury leaching to the concrete mix. In fact, the level of mercury in leachate
from fly ash material is so low that it is nearly undetectable. The importance of using
valid leaching protocols when evaluating complex inorganic materials was taken into
39
account throughout the study and complex chemical reactions that could occur were
restricted before they could have an impact on the generation of leachate.
4.2 Recommendations
Several additional studies have found similar results to the analysis of this
research experiment. Leaching studies conducted at a structural fill site in Minnesota and
an embankment in Illinois indicated that even though some groundwater contamination
had occurred, only very small localized changes in trace element concentration were
detected off site after 8 years. Similarly, nearly 15 years after ash was used to construct a
highway overpass embankment, sampling and analysis of groundwater, soils and
vegetation in another study showed only slightly elevated levels of some constituents
related to fly ash. A University of Pittsburg study conducted environmental and physical
testing of concrete made from fly as and concluded that in all areas, leachate
compositions of 17 different elements show fly as materials to be nonhazardous and
likely environmentally benign.
Throughout the course of this research study, questions about the utilization
accuracy of the TCLP and SPLP methods have been uncovered. One study suggested
that the solutions used to simulate the leachate were highly inadequate. Another study
concluded that the solid to liquid ratio requirement from the EPA test methods were in
accurate. These issues could negatively effect the results of this study – if the solutions
were inadequate in leaching the fly ash material, an incorrect measurement of the
elements in the leachate could be reported.
40
It is recommended that fly ash in concrete be continually monitored for future
mercury leachate. A study focusing on the long term effects of leaching on fly ash is also
suggested as a means to determine the degenerative effect of time on the samples.
Though fly ash samples can only simulate the actions of the fly ash materials in concrete,
the results from this study can be extended to provide insight into the overall contribution
of fly ash to concrete structures. In the end, this study recommends that fly ash
utliziation is an economical alternative to Portland cement that will not cause
environmental or public harm.
41
CHAPTER 5
REFERENCES
American Concrete Pavement Association, Pavement Technology, January, 2006.
American Coal Ash Association, Coal Combustion product Production and Use, 2002.
Cannon, R.W.; Concrete Institute, 1968.
Electric Power Research Institute, Mercury Emissions From Concrete Containing Fly
Ash and Mercury-Loaded Powdered Activated Carbon, December, 2003.
Galbreath, K.C.; Zygarlicke, C.J. Mercury Transformations in Coal Combustion Flue Gas.
Fuel Processing Technol., 2000, 65-66, 289.
Gibb, W. H.; Clarke, F.; Mehta, A. K. The Fate of Coal Mercury During Combustion.
Fuel Processing Technol., 2000, 65-66, 365.
42
Garboczi, E.J., and D.P. Bentz, "Fundamental Computer Simulation Models for Cement-
Based Materials", 1990.
Goldman, A., and Bentur, A., "Bond Effects in High- Strength Silica-Fume Concretes",
1989.
Hansen, T.C.; Cement Concrete Res. 1990.
Roberts, L.R., "Microsilica in Concrete I", in Materials Science of Concrete Vol. 1, 1989. Sybertz, F., "Comparison of Different Test Methods for Testing the Pozzolanic Activity
of Fly Ashes", ACI SP 114-22, Fly Ash, Silica Fume, and Natural Pozzolans in
Concrete, 1989.
U.S. Environmental Protection Agency, Analysis of Emissions Reduction Options for the
Electric Power Industry, March, 1999.
Zhang, M-H; American Concrete Institute Materials Journal, 2001.
Uchikawa, H., "Similarities and Discrepancies of Hardened Cement Paste, Mortar, and
Concrete from the Standpoint of Composition and Structure", 1988.
Zimbelman, R., "A Contribution to the Problem of Cement-Aggregate Bond", 1985.
43
APPENDIX Mercury Concentration Sample Data
44
45
Analyte Element Concentration
46
47
48
49
50
51
52
53
54
55